Perovskite solar cell and preparation method thereof

Abstract

The invention discloses a perovskite solar cell and a preparation method thereof, the perovskite solar cell is characterized in that a second ITO conductive layer is arranged at the top of a first ITO conductive layer and at the bottom of a top gate electrode, and the work function of the second ITO conductive layer is smaller than that of the first ITO conductive layer; and a third ITO conducting layer is arranged at the bottom of the ITO film layer on the bottom surface of the heterojunction bottom cell and at the top of the back gate electrode, and the work function of the third ITO conducting layer is larger than that of the ITO film layer on the bottom surface of the heterojunction bottom cell. A smooth work function gradient is formed between the two layers of ITO, that is, a built-in energy level slope is constructed between the electron transport layer / hole transport layer and the silver electrode, electrons / holes are guided to flow downhill and uphill more smoothly, and energy loss and accumulation at a single steep interface are reduced; the contact resistance between the ITO with high quality and low work function on the outer layer and the silver electrode is obviously reduced, and the total series resistance of the device is effectively reduced, so that the device has a higher fill factor.

Description

Technical Field

[0001] This invention relates to a photovoltaic cell, and more particularly to a perovskite solar cell with both high transmittance and high conductivity, and a method for preparing the same. Background Technology

[0002] Perovskite solar cells, as an emerging photovoltaic technology, have achieved certified efficiencies exceeding 26%, demonstrating enormous application potential. In classic nip structures, tin oxide (SnO2) is typically used as the electron transport layer, with silver (Ag) or gold (Au) as the top metal electrode. However, this structure suffers from a critical interface problem: the work function of SnO2 (approximately 4.4-5.2 eV) is not perfectly matched with the work function of the commonly used metal electrode Ag (approximately 4.2-5.0 eV). This energy level mismatch forms a Schottky barrier at the SnO2 / Ag interface, leading to the following defects: 1. Increased electron collection resistance: manifested as a decrease in the cell's fill factor; 2. Increased interface recombination: hindered electrons accumulate at the interface, recombine with holes, resulting in open-circuit voltage loss; 3. Stability risks: non-ideal interface contacts may become a weak point in the long-term stability of the device. Currently, the industry commonly uses spin-coating of organic molecules such as PCBM onto the SnO2 surface for interface modification. While this method is effective, the long-term stability of PCBM and its uniformity in large-area fabrication remain challenges. Furthermore, simple surface modification has limited energy level modulation capabilities, making it difficult to perfectly connect work functions with significant differences. Fabricating an ITO thin film as a conductive layer between SnO2 and Ag can also reduce the Schottky barrier between them; however, the ITO film needs to balance good conductivity and high transmittance. Conductivity and transmittance are achieved by adjusting process parameters. Good conductivity requires low oxygen content, while high transmittance requires high oxygen content; a compromise must be found. Moreover, ITO films in perovskite solar cells cannot be fabricated at high temperatures, as high temperatures will damage the underlying perovskite layer, leading to a decrease in the perovskite cell's electrical performance. Therefore, ITO films must be fabricated at room temperature or below 100°C to ensure the integrity of the underlying perovskite layer. Thus, the development of high-transmittance, high-conductivity fabrication processes that can be performed at room temperature or low temperatures is crucial. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to reduce the Schottky barrier at the SnO2 / Ag interface and improve the efficiency of perovskite solar cells without affecting light transmittance, and to provide a perovskite solar cell; another purpose of this invention is to provide a method for preparing the above-mentioned perovskite solar cell.

[0004] Technical Solution: The perovskite solar cell of the present invention comprises, from bottom to top, a back grid electrode, a heterojunction bottom cell, a nickel oxide hole transport layer, a SAM layer, a perovskite light-absorbing layer, a passivation layer, an electron transport layer, a first ITO conductive layer, and a top grid electrode. A second ITO conductive layer is disposed on top of the first ITO conductive layer and at the bottom of the top grid electrode, wherein the work function of the second ITO conductive layer is less than that of the first ITO conductive layer. A third ITO conductive layer is disposed at the bottom of the ITO film layer on the bottom surface of the heterojunction bottom cell and at the top of the back grid electrode, wherein the work function of the third ITO conductive layer is greater than that of the ITO film layer on the bottom surface of the heterojunction bottom cell.

[0005] Furthermore, the work function of the second ITO conductive layer is 4.0-4.2 eV and the thickness is 80-120 nm, while the work function of the first ITO conductive layer is 5.0-5.2 eV and the thickness is 80-120 nm. By controlling the sputtering power and the oxygen content in the sputtering atmosphere, the oxygen content of the second ITO conductive layer is made lower than that of the first ITO conductive layer, thereby making the work function of the second ITO conductive layer lower than that of the first ITO conductive layer, which facilitates the extraction of charge carriers.

[0006] Furthermore, the work function of the third ITO conductive layer is 5.0-5.2 eV and the thickness is 80-120 nm, while the work function of the ITO film layer on the bottom surface of the heterojunction battery is 4.0-4.2 eV and the thickness is 80-120 nm. By controlling the sputtering power and the oxygen content in the sputtering atmosphere, the oxygen content of the third ITO conductive layer is made greater than that of the ITO film layer on the bottom surface of the heterojunction battery, thereby making the work function of the third ITO conductive layer greater than that of the ITO film layer on the bottom surface of the heterojunction battery, which facilitates hole extraction.

[0007] The present invention also provides a method for preparing the above-mentioned perovskite solar cell, comprising the following steps:

[0008] The heterojunction bottom cell was cleaned and dried. An ITO bonding layer was set on the top of the heterojunction bottom cell and an ITO film layer was set on the bottom.

[0009] A nickel oxide hole transport layer, a SAM layer, a perovskite light-absorbing layer, a passivation layer, and an electron transport layer are sequentially formed on the ITO bonding layer at the top of the heterojunction solar cell. The electron transport layer includes a C-type electrode bonded to the passivation layer. 60 The layer and the tin oxide layer on top of it;

[0010] A first ITO film layer is formed on the tin oxide layer, a second ITO film layer is formed on the first ITO film layer, and a third ITO conductive layer is formed on the ITO film layer at the bottom of the heterojunction bottom cell.

[0011] A top gate electrode and a back gate electrode are formed on the second ITO film layer and the third ITO conductive layer, respectively.

[0012] Furthermore, silver electrodes are used for both the top and back gate electrodes.

[0013] Furthermore, the ITO bonding layer on the top of the heterojunction bottom cell, the ITO film layer on the bottom surface, the first ITO film layer, and the second ITO film layer are generated by magnetron sputtering. The target material is ITO, the In:Sn ratio is 90:10, the sputtering atmosphere is Ar and O2, the process pressure is 0.2-0.8 Pa, and the belt speed is 5-10 rpm / min.

[0014] Furthermore, the sputtering temperature of the first ITO film layer and the third ITO conductive layer is room temperature - 100°C, the sputtering power is 100-300W, and the oxygen content in the sputtering atmosphere is 1%-2%; the sputtering temperature of the second ITO film layer and the ITO film layer on the bottom surface of the heterojunction battery is room temperature - 100°C, the sputtering power is 100-300W, and the oxygen content in the sputtering atmosphere is 0.2%-0.5%.

[0015] Furthermore, the oxygen content in the sputtering atmosphere of the ITO connecting layer at the top of the heterojunction bottom cell is 0.2-0.5%, and the thickness is 15-30 nm.

[0016] Furthermore, the nickel oxide hole transport layer is formed by magnetron sputtering and has a thickness of 10-30 nm; the SAM layer is formed by spin coating and has a thickness of 1-2 nm; the perovskite light-absorbing layer is formed by spin coating and has a thickness of 300-500 nm; and the passivation layer is formed by spin coating and has a thickness of 2-5 nm. The nickel oxide hole transport layer, SAM layer, perovskite light-absorbing layer, and passivation layer require annealing treatment.

[0017] Furthermore, in the electron transport layer, C 60 The first layer is generated by vacuum evaporation with a film thickness of 5-20 nm, while the second layer is generated by atomic deposition with a film thickness of 10-30 nm.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. A smooth work function gradient is formed between the two ITO layers, which is equivalent to building a built-in "energy level ramp" between the electron transport layer / hole transport layer and the silver electrode, guiding electrons / holes to flow more smoothly "downhill and uphill", reducing energy loss and accumulation at a single steep interface; 2. The contact resistance between the outer high-quality, low-work-function ITO and the silver electrode is significantly reduced, effectively reducing the total series resistance of the device, thus having a higher fill factor. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the present invention;

[0020] Figure 2This is a schematic diagram of the mask layers used in the magnetron sputtering process for the second and third ITO conductive layers of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0022] Example 1

[0023] like Figure 1 The perovskite solar cell shown includes a back grid electrode 13, a heterojunction bottom cell 1, a nickel oxide hole transport layer 3, a SAM layer 4, a perovskite light-absorbing layer 5, a passivation layer 6, an electron transport layer, a first ITO conductive layer 9, and a top grid electrode 11. It also includes a second ITO conductive layer 10 disposed on top of the first ITO conductive layer 9 and at the bottom of the top grid electrode 11, and a third ITO conductive layer 12 disposed at the bottom of the ITO film layer on the bottom surface of the heterojunction bottom cell 1 and on top of the back grid electrode 13. The back grid electrode 13 and the top grid electrode 11 are silver electrodes. The electron transport layer includes a C electrode bonded to the passivation layer 6. 60 Layer 7 and its top tin oxide layer 8; the heterojunction bottom cell 1 combines the silicon cell and perovskite through the front ITO connecting layer 2. The work function of the second ITO conductive layer 10 is 4.0-4.2 eV and the thickness is 80-120 nm, the work function of the first ITO conductive layer 9 is 5.0-5.2 eV and the thickness is 80-120 nm, the work function of the third ITO conductive layer 12 is 5.0-5.2 eV and the thickness is 80-120 nm, and the work function of the ITO film layer on the bottom surface of the heterojunction bottom cell 1 is 4.0-4.2 eV and the thickness is 80-120 nm. The top gate electrode 11 and the back gate electrode 13 are silver electrodes. The thickness of the ITO connecting layer 2 on the top of the heterojunction bottom cell 1 is 15-30 nm. The nickel oxide hole transport layer 3 is formed by magnetron sputtering and has a thickness of 10-30 nm. The SAM layer 4 is formed by spin coating and has a thickness of 1-2 nm. The perovskite light-absorbing layer 5 is formed by spin coating and has a thickness of 300-500 nm. The passivation layer 6 is formed by spin coating and has a thickness of 2-5 nm. In the electron transport layer, C... 60 Layer 7 is formed by vacuum evaporation with a thickness of 5-20 nm, and layer 8, tin oxide, is formed by atomic deposition with a thickness of 10-30 nm. By controlling the sputtering power and the oxygen content in the sputtering atmosphere, the work function of different ITO films is adjusted to establish a conductive layer with a work function gradient along the electron or hole transport path, allowing for smooth electron extraction.

[0024] The above-mentioned method for preparing perovskite solar cells includes the following steps:

[0025] (1) Clean and dry the heterojunction bottom cell 1. The heterojunction bottom cell 1 includes a silicon substrate and its front ITO bonding layer 2 and bottom ITO film layer. The ITO bonding layer 2 and the bottom ITO film layer are fabricated by magnetron sputtering at room temperature. The ITO bonding layer 2 uses ITO as the target material, wherein the ratio of In to Sn is 90:10, the sputtering power is 210W, the sputtering atmosphere is Ar and O2, wherein the oxygen content is 0.4%, the process pressure is 0.2Pa, and the transfer speed is 8rpm / min (magnetron sputtering can also be selected). The temperature was room temperature to 100℃, the sputtering power was 100-300W, the process pressure was 0.2-0.8Pa, and the transfer speed was 5-10rpm / min, resulting in a film thickness of 20nm; the bottom ITO film layer, using ITO as the target material, with an In:Sn ratio of 90:10, a sputtering power of 210W, a sputtering atmosphere of Ar and O2 with an oxygen content of 0.4%, a process pressure of 0.2Pa, and a transfer speed of 8rpm / min, resulted in a film thickness of 80nm and a work function of 4.0eV;

[0026] (2) A nickel oxide hole transport layer 3 with a thickness of 20 nm was deposited on the ITO connection layer 2 on the front side of the heterojunction cell by magnetron sputtering and annealed at 200 °C for 60 minutes.

[0027] (3) A SAM layer 4 with a thickness of 2 nm was prepared on the nickel oxide hole transport layer 3 by spin coating and annealed at 110 °C for 10 minutes (the annealing process can be selected as 80-120 °C for 5-20 minutes).

[0028] (4) A perovskite light-absorbing layer 5 with a thickness of 300 nm was prepared on the SAM layer 4 by spin coating and annealed at 120 °C for 10 minutes (the annealing process can be selected as: annealing at 100-150 °C for 10-60 minutes).

[0029] (5) A passivation layer 6 with a thickness of 3 nm was prepared on the perovskite light-absorbing layer 5 by spin coating and annealed at 100°C for 10 minutes (the annealing process can be selected as annealing at 80-120°C for 5-20 minutes).

[0030] (6) An electron transport layer is prepared on the passivation layer 6. The electron transport layer includes C 60 Layer 7 and tin oxide layer 8, wherein C 60 Layer 7 was prepared by vacuum evaporation and has a film thickness of 10 nm. Tin oxide layer 8 was prepared by atomic deposition (ALD) and has a film thickness of 15 nm.

[0031] (7) The first ITO conductive layer 9 was prepared on the tin oxide layer 8 by magnetron sputtering. ITO was used as the target material, and the ratio of In to Sn was 90:10. The sputtering temperature was room temperature, the sputtering power was 210W, the sputtering atmosphere was Ar and O2 with an oxygen content of 1.5%, the process pressure was 0.2Pa, the transfer speed was 8rpm / min, the film thickness was 80nm, and the work function was 5.0eV.

[0032] (8) On top of the first ITO conductive layer 9, a method is used as follows: Figure 2 The mask 14 shown is used to prepare a second ITO conductive layer 10 at the position of the top gate electrode 11 by magnetron sputtering. ITO is used as the target material, wherein the ratio of In to Sn is 90:10, the sputtering temperature is room temperature, the sputtering power is 210W, the sputtering atmosphere is Ar and O2 with an oxygen content of 0.4%, the process pressure is 0.2Pa, the transfer speed is 8rpm / min, and the resulting film thickness is 80nm with a work function of 4.0ev.

[0033] (9) On the ITO film layer on the bottom surface of the heterojunction bottom cell 1, the following is used: Figure 2 The mask shown is used to fabricate a third ITO conductive layer 12 at the back gate electrode 13 using magnetron sputtering. ITO is used as the target material, with an In:Sn ratio of 90:10. The sputtering temperature is room temperature, the sputtering power is 210W, the sputtering atmosphere is Ar and O2 with an oxygen content of 1.5%, the process pressure is 0.2Pa, the transfer speed is 8rpm / min, and the resulting film thickness is 80nm with a work function of 5.0eV.

[0034] (10) A top gate electrode 11 is formed on the second ITO conductive layer 10, and a back gate electrode 13 is formed on it.

[0035] A second ITO conductive layer is placed on top of the first ITO conductive layer and at the bottom of the top gate electrode. This ITO conductive layer, with its gradually decreasing work function, creates a "downhill" energy path, achieving a continuous energy level transition from the electron transport layer to the metal electrode. This significantly reduces the contact barrier, allowing electrons to be collected "seamlessly." The smooth energy level structure effectively suppresses electron accumulation and recombination at the interface, thus significantly improving the cell's open-circuit voltage (Voc) and fill factor (FF). A third ITO conductive layer is placed at the bottom of the ITO film layer on the bottom surface of the heterojunction cell and at the top of the back gate electrode. This ITO conductive layer, with its gradually increasing work function, creates an "uphill" energy path for hole flow from the transport layer to the metal electrode through the spatial gradient design of the work function. This allows for efficient hole extraction, and the high-quality, low-resistance ITO layer helps reduce interface contact resistance, enabling smooth hole discharge. This results in a higher fill factor, higher open-circuit voltage, and lower series resistance for the entire device, ultimately improving conversion efficiency and stability. If the work function of the ITO conductive layer is set to be the same or the gradient of the work function changes in opposite directions, electrons / holes will not be able to be successfully exported or effectively collected, resulting in a decrease in device efficiency.

[0036] In addition, as a mature transparent electrode material, ITO's sputtering process is compatible with existing semiconductor processes, making it easy to achieve large-area, uniform fabrication. It has strong process compatibility and better stability than organic interface layers.

[0037] Comparative Example 1

[0038] The difference compared to Example 1 is that the second ITO conductive layer and the third ITO conductive layer are not provided.

[0039] Compared to Example 1, Comparative Example 1 only has one layer of ITO film on both sides, resulting in poor electron contact at the top: a large Schottky barrier is formed between the high work function ITO and the low work function Ag electrode, severely hindering electron extraction and leading to high contact resistance and severe interfacial recombination. Poor hole contact at the bottom: the low work function ITO mismatches with the hole transport end of the silicon heterojunction, resulting in limited hole extraction; at the same time, the contact with the back Ag electrode may also be unsatisfactory. Significant carrier accumulation and recombination at both ends lead to a lower open-circuit voltage (Voc), fill factor (FF), and high series resistance (Rs) in the device, resulting in low device efficiency.

[0040] Comparative Example 2

[0041] Compared with Example 1, the difference is that only the second ITO conductive layer is provided, and the third ITO conductive layer is not provided.

[0042] Compared to Example 1 and Comparative Example 1, Comparative Example 2 only has one ITO thin film on the front side, resulting in improved top performance but no optimization of bottom performance. The problem with the bottom hole exit interface (as described in Comparative Example 1) is exactly the same, leading to hole accumulation and recombination on the back side, which will limit further improvement in Voc. While the overall performance is better than Comparative Example 1, it cannot reach the optimal level. This is because the total current of the device is limited by the "slowest" carrier (holes in this case), which limits the upper limit of the overall efficiency.

[0043] Comparative Example 3

[0044] Compared with Example 1, the difference is that only the third ITO conductive layer is provided, and the second ITO conductive layer is not provided.

[0045] Compared to Example 1 and Comparative Example 1, Comparative Example 3 only has one ITO thin film on the back side, resulting in improved bottom performance, while the top becomes the bottleneck: the high barrier at the top electron extraction interface (as described in Comparative Example 1) becomes the main limiting factor. Electrons cannot be effectively collected, leading to severe interface recombination and high series resistance. The overall performance is still better than Comparative Example 1, but the device efficiency is not optimal.

Claims

1. A perovskite solar cell, comprising, from bottom to top, a back grid electrode, a heterojunction bottom cell, a nickel oxide hole transport layer, a SAM layer, a perovskite light-absorbing layer, a passivation layer, an electron transport layer, a first ITO conductive layer, and a top grid electrode, characterized in that, A second ITO conductive layer is disposed on top of the first ITO conductive layer and at the bottom of the top gate electrode, wherein the work function of the second ITO conductive layer is less than that of the first ITO conductive layer; a third ITO conductive layer is disposed at the bottom of the ITO film layer on the bottom surface of the heterojunction bottom cell and at the top of the back gate electrode, wherein the work function of the third ITO conductive layer is greater than that of the ITO film layer on the bottom surface of the heterojunction bottom cell.

2. The perovskite solar cell according to claim 1, characterized in that, The work function of the second ITO conductive layer is 4.0-4.2 eV and the thickness is 80-120 nm, while the work function of the first ITO conductive layer is 5.0-5.2 eV and the thickness is 80-120 nm.

3. The perovskite solar cell according to claim 1, characterized in that, The third ITO conductive layer has a work function of 5.0-5.2 eV and a thickness of 80-120 nm, while the ITO film layer on the bottom surface of the heterojunction battery has a work function of 4.0-4.2 eV and a thickness of 80-120 nm.

4. A method for preparing a perovskite solar cell according to claim 1, characterized in that, Includes the following steps: The heterojunction bottom cell was cleaned and dried. An ITO bonding layer was set on the top of the heterojunction bottom cell and an ITO film layer was set on the bottom. A nickel oxide hole transport layer, a SAM layer, a perovskite light-absorbing layer, a passivation layer, and an electron transport layer are sequentially formed on the ITO bonding layer at the top of the heterojunction solar cell. The electron transport layer includes a C-type electrode bonded to the passivation layer. 60 The layer and the tin oxide layer on top of it; A first ITO film layer is formed on the tin oxide layer, a second ITO film layer is formed on the first ITO film layer, and a third ITO conductive layer is formed on the ITO film layer at the bottom of the heterojunction bottom cell. A top gate electrode and a back gate electrode are formed on the second ITO film layer and the third ITO conductive layer, respectively.

5. The method for preparing a perovskite solar cell according to claim 4, characterized in that, The ITO bonding layer on the top of the heterojunction bottom cell, the ITO film layer on the bottom surface, the first ITO film layer, and the second ITO film layer are generated by magnetron sputtering.

6. The method for preparing a perovskite solar cell according to claim 5, characterized in that, The sputtering temperature of the first ITO film layer and the third ITO conductive layer is room temperature - 100°C, the sputtering power is 100-300W, and the oxygen content in the sputtering atmosphere is 1%-2%; the sputtering temperature of the second ITO film layer and the ITO film layer on the bottom surface of the heterojunction battery is room temperature - 100°C, the sputtering power is 100-300W, and the oxygen content in the sputtering atmosphere is 0.2%-0.5%.

7. The method for preparing a perovskite solar cell according to claim 5, characterized in that, The oxygen content of the ITO bonding layer at the top of the heterojunction bottom cell is 0.2-0.5% and the thickness is 15-30 nm in the sputtering atmosphere.

8. The method for preparing a perovskite solar cell according to claim 4, characterized in that, The thickness of the nickel oxide hole transport layer is 10-30 nm, the thickness of the SAM layer is 1-2 nm, the thickness of the perovskite light-absorbing layer is 300-500 nm, and the thickness of the passivation layer is 2-5 nm.

9. The method for preparing a perovskite solar cell according to claim 8, characterized in that, The nickel oxide hole transport layer, SAM layer, perovskite light-absorbing layer, and passivation layer require annealing.

10. The method for preparing a perovskite solar cell according to claim 4, characterized in that, C in the electron transport layer 60 The first layer is generated by vacuum evaporation and has a film thickness of 5-20 nm, while the second layer is generated by atomic layer deposition and has a film thickness of 10-30 nm.

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